Heterogeneous and Homogeneous Routes in Water Oxidation Catalysis Starting from CuII Complexes with Tetraaza Macrocyclic Ligands. Issue 8 (11th March 2016) - Prevedello, Andrea
Abstract: Since the first report in 2012, molecular copper complexes have been proposed as efficient electrocatalysts for water oxidation reactions, carried out in alkaline/neutral aqueous media. However, in some cases the copper species have been recognized as precursors of an active copper oxide layer, electrodeposited onto the working electrode. Therefore, the question whether copper catalysis is molecular or not is particularly relevant in the field of water oxidation. In this study, we investigate the electrochemical activity of copper(II) complexes with two tetraaza macrocyclic ligands, distinguishing heterogeneous or homogeneous processes depending on the reaction media. In an alkaline aqueous solution, and upon application of an anodic bias to working electrodes, an active copper oxide layer is observed to electrodeposit at the electrode surface. Conversely, water oxidation in neutral aqueous buffers is not associated to formation of the copper oxide layer, and could be exploited to evaluate and optimize a molecular, homogeneous catalysis. Abstract : The dark side of copper : Homogeneous water oxidation electrocatalysis promoted by copper (II) complexes with tetraaza macrocyclic ligands occurs in neutral aqueous media with turnover frequency up to 7 s ‐1, while heterogeneous routes are predominant in alkaline conditions, involving the formation of active copper oxide at the electrode surface.